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NIOSH Responses to SCA’s Thorium Report of May 8, 2012 

May 29, 2012 

SC&A comment 1: 

Was access to, and working with, the thorium-containing materials controlled by physical barriers and/or 

procedural requirements? 

NIOSH response 1: 

The redrumming effort occurred in a remote part of the site (near the future location of Building 21 – the 

thorium sludge storage building), geographically removed from other site activities. Former workers 

have anecdotally told NIOSH that controls (exclusion zones, health physics monitoring, respiratory 

protection, etc.) were established and that the workers involved were on a routine urinalysis program 

(which is supported by the urinalysis records). Therefore, it is highly unlikely that a worker would have 

visited this work location without being on at least gross alpha urinalysis. 

SC&A comment 2: 

Were only persons directly involved with handling the material allowed in the area, or could there have 

been other personnel, such as craft workers, maintenance workers, grounds keeper, etc., that may have 

worked around the material, but were not considered part of the thorium-handling crew? Exposures could 

have occurred not only during the periods the material was being handled, but also during dormant 

periods when no specific activity was taking place, and no health physics oversight was in place; thorium 

bioassays would not have been available for these types of workers under those circumstances. 

NIOSH response 2: 

Craft and maintenance workers were in fact the personnel performing this project. It involved Hyster 

operators and laborers, as well as health physics monitors. It is unlikely that exposures occurred during 

the “dormant” periods. The drums were stored outside in a geographically remote part of the site 

removed from other site activities. Redrumming occurred in the warm weather months, and ceased in the 

winter months. While it would not be physically impossible for some worker to visit this remote location 

in the dead of winter when no activity was being performed, reasons for doing so are not obvious. 

Furthermore, the material was contained in drums. While it is true that some drums began rusting, hence 

the need for redrumming, the airborne exposure potential from material so stored would have been 

minimal unless the material was disturbed (e.g. redrumming). 

SC&A comment 3: 

What situation or procedure triggered the need to obtain urine samples and have them analyzed for 

thorium and the results recorded? 

NIOSH response 3: 

As with other radionuclides at Mound, work with 232Th triggered collection of urine samples. Workers 

involved in this activity were on a routine urinalysis program. 

This is a working document prepared by NIOSH or its contractor for use in discussions with the ABRWH or its Working Groups or 

Subcommittees. Draft, preliminary, interim, and White Paper documents are not final NIOSH or ABRWH (or their technical 

support and review contractors) positions unless specifically marked as such. This document represents preliminary positions taken 

on technical issues prepared by NIOSH or its contractor. 

NOTICE: This report has been reviewed to identify and redact any information that is protected by the Privacy Act 5 USC §552a 

and has been cleared for distribution. 
 

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SC&A comment 4: 

Was a list of personnel working with or around thorium-containing materials maintained? Relying on 

recorded thorium bioassays and/or applying a coworker model can only be used if it can reasonably be 

assured that the potentially thorium-exposed workers were bioassayed or identifiable for coworker dose 

application, unless the coworker dose is applied to all unmonitored workers. 

NIOSH response 4: 

NIOSH is aware of no list of workers on the thorium redrumming project beyond what can be assembled 

from the bioassay records. Also see NIOSH response 5. 

SC&A comment 5: 

ORAUT-TKBS-0016-5 states: 

Page 30 – Th-230

230 

Primary Th bioassay records consisted of a logbook, and apparently duplicate records 

in a brown notebook. Count data were typically recorded on Form O-318 followed by an 

230 

“I” or “Io.” Secondary Th results started as weekly reports on March 17, 1958. Weekly 

230 

reports included Name, Isotope, and Result. Prior to 1958, secondary Th results were 

reported on Form O-634 including Name, Badge Number, Date, Type of Analysis, 

Isotope, and Result. However, some secondary documents have problems with reporting 

units. Some results are reported to be cph [counts per hour] per 24-hour sample when 

primary records indicate that they are actually cpm [counts per minute] per aliquot. The 

ORAU database should therefore be considered a secondary record extracted from 

primary records. 

Page 32 – Th-232 

Thorium-232 records are diverse due to programs conducted for many years. Primary

232 

Th bioassay data were entered into a small brown spiral notebook marked “RadiumThorium” and “Radium-Thorium Separation from 8/15/1955 to 2/2/1959 (Meyer 1992). 

Additional primary 232Th bioassay data were recorded in a large hardcover record book. 

However, the first 38 pages from this record book were removed from 7/6/59 to 1/9/61, 

7/13/64 to 11/15/64 and 5/30/65 to 6/6/65. These record books apparently do not contain 

true primary data, but calculated results such as cpm excreted per day. Secondary records 

232 

in weekly reports contained Th results as cpm/24-hr samples beginning March 17, 

1958. In August 1959, secondary results were reported on form O-756. The ORAU 

232 

database is a record of secondary Th bioassay data extracted from other primary 

records (ORAU 2003e). [Emphasis added.] 

From this information, it is not apparent that the dose reconstructor has access to copies of all the original 

data sheets, or where they are located. SC&A’s scan of some of the DOE files located several of these 

forms with thorium bioassay data recorded. However, there does not appear to be much assurance that all 

the primary data are available to the dose reconstructor. 

This is a working document prepared by NIOSH or its contractor for use in discussions with the ABRWH or its Working Groups or 

Subcommittees. Draft, preliminary, interim, and White Paper documents are not final NIOSH or ABRWH (or their technical 

support and review contractors) positions unless specifically marked as such. This document represents preliminary positions taken 

on technical issues prepared by NIOSH or its contractor. 

NOTICE: This report has been reviewed to identify and redact any information that is protected by the Privacy Act 5 USC §552a 

and has been cleared for distribution. 
 

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NIOSH response 5: 

The quote from ORAUT-TKBS-0016-5 page 30 is not relevant as it deals with ionium (230Th), while the 

subject of NIOSH’s paper was reconstruction of dose from 232Th. The record books in question are 

available in the SRDB. SC&A has seen for themselves that thorium bioassay results are included in the 

DOE files. It is not possible to prove a negative i.e. NIOSH cannot prove that there are no records 

beyond those captured in the SRDB and claimant files. However, it is worth considering that the 

majority (if not the entirety) of the thorium redrumming effort occurred in or before 1959. There is 

already a SEC class at Mound including all workers for this time period. The effect of disregarding the 

thorium bioassay records would be to deny the thorium doses calculated from these data from workers 

who don’t qualify for the existing SEC. This is not claimant favorable, and since we demonstrated that 

thorium doses can be reconstructed in our Retrospective Dose Reconstruction for Thorium-232 Activities 

at the Mound Laboratory, (April, 2012) in NIOSH’s judgment disregarding this data is not scientifically 

justified. 

SC&A comment 6: 

In addition to the drummed material from United Lead Corporation (ULC), Mound also received 

thorium-containing materials from the St. Louis Airport, according to page 15 of ORAUT-TKBS-0016-2 

(ORAUT 2004): 

SW building was used in the Cotter Concentrate (St. Louis Airport Cake) starting in the early 

1970s and terminated late in that decade. Pilot plant operations in SW were to recover Th-230 

and Pa-231. 

The Cotter concentrate contained 99.9 g/drum of Th-232 and 11.1 g/drum of Th-230, according to page 

16. 

NIOSH response 6: 

The Cotter concentrate material actually came from the Cotter Corporation in Canon City, Colorado. 

The Cotter Concentrate program has been extensively discussed in NIOSH Evaluation of Data Adequacy 

and Completeness Issues at the Mound Laboratory (August, 2011) [see NIOSH Responses 6, 9, 52, and 

56 in that document]. 

SC&A comment 7: 

Additionally, thorium was used in other areas at Mound as stated on page 12 of ORAUT-TKBS-0016: 

238 

Thorium-232 was often substituted for Pu compounds for modeling purposes in 

research and development, because this isotope was less expensive and less hazardous, 

238 232 

and had physical characteristics similar to Pu. It is possible, therefore, to find Th 

238 

compounds identical to the Pu compounds. 

These were not included in the paper that SC&A could find, and most likely not in the cleanup date of 

September 1975 as stated on page 20 of the paper. Although the drummed material from ULC most 

likely presented the greatest exposure potential, the issue of thorium exposure/monitoring did not go 

completely away in mid-1975. These other sources of thorium, and thorium contamination present during 

This is a working document prepared by NIOSH or its contractor for use in discussions with the ABRWH or its Working Groups or 

Subcommittees. Draft, preliminary, interim, and White Paper documents are not final NIOSH or ABRWH (or their technical 

support and review contractors) positions unless specifically marked as such. This document represents preliminary positions taken 

on technical issues prepared by NIOSH or its contractor. 

NOTICE: This report has been reviewed to identify and redact any information that is protected by the Privacy Act 5 USC §552a 

and has been cleared for distribution. 
 

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decontamination and decommissioning (D&D), are sources that could also result in personnel exposures 

and require bioassay data for DR. 

NIOSH response 7: 

Just as was the case for thorium at Rocky Flats, where thorium was used as a stand-in for plutonium, the 

exposure potential from these applications would be minimal. While NIOSH never asserted, “the issue 

of thorium exposure/monitoring did not go completely away in mid-1975”, we agree with SC&A’s 

assessment that the monazite sludge redrumming program would have been the activity performed at 

Mound with the highest thorium-232 internal dose potential. 

However, as extensively discussed in NIOSH Evaluation of Data Adequacy and Completeness Issues at 

the Mound Laboratory (August, 2011) [see especially NIOSH Response 63], the gross alpha procedure 

used at Mound was capable of isolating actinium, neptunium, americium, curium, and thorium. As 

described in NIOSH’s Retrospective Dose Reconstruction for Thorium-232 Activities at the Mound 

Laboratory, (April, 2012), nuclide specific procedures could be (and were) performed to determine 

which of these nuclides were present. But in the absence of nuclide-specific results, the results of gross 

alpha urinalyses can be conservatively attributed to whichever of these nuclides is plausibly present, and 

gives the highest organ-specific dose for the dose reconstruction being performed. This is the way 

NIOSH handles gross alpha urinalysis results at every other facility, and the procedures used at Mound 

will be no different. In any case, the twenty dose-reconstructions performed in NIOSH’s Retrospective 

Dose Reconstruction for Thorium-232 Activities at the Mound Laboratory, (April, 2012) indicate that 

doses calculated by assuming the activity in the sample came from thorium-232 would be comparable to 

those calculated by assuming plutonium-238. 

This is a working document prepared by NIOSH or its contractor for use in discussions with the ABRWH or its Working Groups or 

Subcommittees. Draft, preliminary, interim, and White Paper documents are not final NIOSH or ABRWH (or their technical 

support and review contractors) positions unless specifically marked as such. This document represents preliminary positions taken 

on technical issues prepared by NIOSH or its contractor. 

NOTICE: This report has been reviewed to identify and redact any information that is protected by the Privacy Act 5 USC §552a 

and has been cleared for distribution.